Field of the Invention
This application relates to the field of lighting technology, and, in particular to lighting fixtures, and is intended for use in domestic and industrial multipurpose lighting instruments.
Description of the Related Art
The main distinctive feature of the LED lamp is distribution of its light flux in the environment. Subject to shapes and dimensions generally accepted for incandescent lamps, the LED lamp provides uniformly distributed diffused light, and unlike most modern lamps, the beam angle does not correspond with lamps replaced thereby.
Thus, a conventional lighting LED lamp includes a base, a transition element (insulator) connected therewith, which is made of dielectric plastic with an additional cavity in the middle. A power supply for lamp operation in electrical networks is located therein, which is connected with an LED module made on a printed circuit board with a heat-conducting metal base and mounted on a radiator. The radiator is made as rod-shaped profile of a complex cross section having side planes pointed at different directions, on which LED modules are placed. The radiator is placed within a diffuser made of plastic which is close to glass in terms of optical performance. The LED modules on each radiator face are placed in front of diffuser sections located between radial projections on the diffuser (see US Patent Publication No. 2012/0313518).
The process of generating distributed diffused light in this LED lamp is such that light from the LED modules passes through the thin transparent plastic wall into the environment, while a portion of the light falls on walls of radial projections and is reflected from their surface. Thus, combinative lighting of the space in the area of 360° around the diffuser is ensured.
The diffuser has a complex spatial shape of a shell with radial ribs, such that the shell center opposite to the base has a through hole for heat removal from the radiator. However, this heat removal method is inefficient because it does not ensure removal of heat from the entire surface of such a rod-shaped radiator. At the same time, the radiator's bottom is spatially adjacent to the power supply of the LED modules located in the base. Thus, the bottom of the radiator is constantly overheated, while heat removal from the radiator top through the fixed orifice using convection in the diffuser is not very efficient. Presence of excessive heat in the radiator bottom results in that heat affects diffuser plastic. Even when using such plastic as polycarbonate (light permeability and transparence are up to 86%) resistant to a wide range of high temperatures (up to 120° C.), constant heating leads to material structure darkening, which impacts on diffusion quality of LED light flux. Special coatings, which reduce impact of heat radiation on the material structure are used for polycarbonate, but these coatings cannot always be used for lighting technology.
It is known that efficiency factor of powerful LEDs is a higher than that of incandescent lamps. On the other hand, most of energy consumed by LEDs (about 75%) is still spent for dissipated heat. Heat emission is increased along with growth of light flux from LED sources. According to estimates provision of efficient heat removal in LED lighting technology is one of the most crucial problems that faces developers and manufacturers of these products today.
Unlike conventional incandescent and gas discharge lamps, modern LEDs are sensitive to high temperatures:
First, when a LED is overheated, its efficiency is reduced, its light flux is weakened, its color temperature is changed, and its service life can decrease considerably;
Second, luminosity intensity is decreased approximately by 15% at the temperature of 80° C. as compared to intensity at the room temperature. As a result, the lighting fixture with twenty LEDs at a temperature of 80° C. can have light flux equivalent to the flux of seventeen LEDs at the room temperature. Intensity of LED light may be reduced by 40% at the transition temperature of 150° C.
Third, LEDs have a negative temperature factor of forward voltage, i.e., forward voltage of LEDs is reduced upon a temperature increase. Usually this factor comprises −3 to −6 mV/K, that is why forward voltage of a standard LED may comprise 3.3 V at +25° C. and not more than 3 V at +75° C. If the power supply does not allow reducing current on LEDs, this may result in further overheating and breakdown of LEDs. Moreover, many power supplies for LED lighting fixtures are designed for the operating temperature of up to +70° C.
Therefore, it is important to provide the temperature of not more than 80° C. both in the p-n-junction area and in the power supply area for efficient operation of LED devices. Failure to observe recommended temperature conditions can result in light quantity and quality loss, increased costs of the LED device, as well as reduction of service life of a lighting device.